The present invention generally relates to a composition of citric acid based emulsifiers for oilfield drilling applications exhibiting low fluorescence. The compositions of the present invention are particularly useful in oilfield drilling applications.
Drilling generally occurs in two phases: exploration and development. Exploration activities are those operations involving the drilling of wells to locate hydrocarbon bearing formations and to determine the size and production potential of hydrocarbon reserves. Development activities involve the drilling of production wells once a hydrocarbon reserve has been discovered and evaluated.
Drilling for oil and gas is generally performed by rotary drilling methods that use a circularly rotating drill bit that grinds through the earth's crust as it descends. Drilling fluids are pumped down through the drill bit via a pipe that is connected to the bit, and serve to cool and lubricate the bit during drilling. The rock chips that are generated as the bit drills through the earth are termed drill cuttings. The drilling fluid also serves to transport the drill cuttings back up to the surface through the space between the drill pipe and the well wall, termed the annulus). The drilling fluid also controls downhole pressure and stabilizes the well bore.
As drilling progresses, large casing pipes called are inserted into the well to line the well wall. Drilling continues until the hydrocarbon bearing formations are encountered. In areas where drilling fluids and drill cuttings are allowed to be discharged under the current regulations, well depths range from approximately 1219 to 3658 meters deep, and it takes approximately 20 to 60 days to complete drilling.
On the surface, the drilling fluid and drill cuttings undergo an extensive separation process to remove as much fluid from the cuttings as possible. The fluid is then recycled into the system, and the cuttings become a waste product. The drill cuttings retain a certain amount of the drilling fluid that is discharged or disposed with the cuttings. Drill cuttings are discharged by the shale shakers and other solids separation equipment. Drill cuttings are also cleaned out of the mud pits and from the solid separation equipment during displacement of the drilling fluid system. Intermittently during drilling, and at the end of the drilling process, drilling fluids may become wastes if they can no longer be reused or recycled.
In the relatively new area of deepwater drilling, generally greater than 914 meters water depth, new drilling methods are evolving which can significantly improve drilling efficiencies and thereby reduce the volume of drilling fluid discharges as well as reduce non-water quality effects of fuel and steel consumption and air emissions. Subsea drilling fluid boosting, referred to as subsea pumping is one such technology. Rotary drilling methods are generally performed as described with the exception that the drilling fluid is energized or boosted by use of a pump at or near the seafloor. By boosting the drilling fluid, the adverse effect on the wellbore caused by the drilling fluid pressure from the seafloor to the surface is eliminated, thereby allowing wells to be drilled with as much as a 50% reduction in the number of casing strings generally required to line the well wall. Wells are drilled in less time, including less trouble time. To enable the pumping of drilling fluids and cuttings to the surface, some drill cuttings, larger than approximately one-fourth of an inch, are separated from the drilling fluid at the seafloor since these cuttings cannot reliably be pumped to the surface. The drill cuttings that are separated at the seafloor are discharged through an eductor hose at the seafloor within a 91 meter radius of the well site. For purposes of monitoring, representative samples of drill cuttings discharged at the seafloor can be transported to the surface and separated from the drilling fluid in a manner similar to that employed at the seafloor. The drilling fluid, which is boosted at the seafloor and transports most of the drill cuttings back to the surface, is processed as described in the general rotary drilling methods described above in this section.
Once the target formations have been reached, and a determination made as to which have commercial potential, the well is made ready for production by a process termed “completion”. Completion involves cleaning the well to remove drilling fluids and debris, perforating the casing that lines the producing formation, inserting production tubing to transport the hydrocarbon fluids to the surface, and installing the surface wellhead. The well is then ready for production, or actual extraction of hydrocarbons.
Drilling fluids and drill cuttings are the most significant wastestreams from exploratory and development well drilling operations. Recently proposed regulations establish discharge limitations for drilling fluids in areas where drilling fluids and drill cuttings are allowed for discharge. These discharge areas are the offshore waters beyond 4.8 kilometers from shore except the offshore waters of Alaska which has no 4.8 kilometer discharge restriction, and the coastal waters of Cook Inlet, Ak. Drilling is currently active in three regions in these discharge areas: (i) the offshore waters beyond three miles from shore in the Gulf of Mexico (GOM), (ii) offshore waters beyond three miles from shore in California, and (iii) the coastal waters of Cook Inlet, Ak. Offshore Alaska is the only other area where drilling is active and effluent guidelines allows discharge. However, drilling wastes are not currently discharged in the Alaska offshore waters. Increased activity in the deepwater increases the usefulness of synthetic based drilling fluids. Operators drilling in the deepwater cite the potential for riser disconnect in floating drill ships, which favors synthetic fluids; higher daily drilling cost which more easily justifies use of more expensive synthetic based fluids; and greater distance to barge drilling wastes that may not be discharged.
As a result of recently proposed regulations, it is desirable to provide drilling fluids having low fluorescence. Fluorescence is a relative brightness test and discharged drilling fluids having low fluorescence are less likely to impart a sheen to the ocean's surface. Accordingly, it is the primary object of the present invention to provide citric acid based emulsifiers for oilfield drilling applications exhibiting low fluorescence.